The new regulations to reduce sulfur content in fossil fuels such as gasoline and diesel bring the search for new alternatives that are substantially different from the catalytic hydrogenation process, which is fully established in refineries [Speight J. G. Kirk-Othmer in Encyclopedia of Chemical Technology. A. Seidel (Ed), Volume 18, John Wiley & Sons, Inc., Hoboken, N.J., 2007, pp. 1-49]. This process operates at relatively high pressures and requires significant amounts of hydrogen, which are required high capital investment and operating costs. This is another reason for the search for new technologies that do not use the conventional hydrotreating.
Among the alternative processes that are not based on hydrotreating, is the adsorption of sulfur compounds on solid adsorbents [U.S. Pat. No. 6,274,031 issued to Phillips Petroleum and U.S. Pat. No. 5,730,860, this process is known as Pritchard] and the removal of sulfur compounds in a liquid phase immiscible with naphtha. There are alternative processes such as oxidative extraction [Sampanthar J. et al. Appl. Catal. B. 2005, 63, 85], complexation [Macauda M. et al. Ind. Eng Chem Res 2004, 43, 7843; Sevignon M. et al. Green Chem 2005, 7, 413]; biodesulfuratión [Li F. et al. Appl. Environ. Microbiol. 2005, 63, 85]; and ultrasonic treatment [U.S. Pat. No. 6,827,844]; all of them have not been developed sufficiently to be tested on an industrial scale.
Desulfurization technology based on liquid-liquid extraction of sulfur compounds or extractive desulfurization, EDS for its acronym in English, in the first instance, is attractive from an economic point of view, lower capital investment and low operating costs, usually at or near ambient temperature and ambient pressure. However, finding the appropriate solvent for extraction is one of the problems to overcome, mainly due to the partial miscibility of organic solvents with hydrocarbons [U.S. Pat. No. 7,001,504]. Among the most widely studied organic solvents are the polyalkylene glycols and polyalkylene glycol ethers, but its performance has not been satisfactory. Another method is to increase the polarity of organic sulfur compounds through partial oxidation and subsequent extraction with a polar solvent [U.S. Pat. Nos. 5,910,440]. 6,160,193 discloses a process of oxidation of sulfur species into sulfoxides or sulfones by microorganisms in an aqueous medium. Another method uses an oxidizing agent such as peroxyacetic acid followed by extraction with an immiscible solvent such as dimethyl sulfoxide [U.S. Pat. No. 6,160,193].
Extractive desulfurization is considered of practical interest considering that the characteristics of the extraction processes are well established technologies and can be operated at ambient conditions. According to the above, one of the main features of the EDS is to find a good extracting of sulfur compounds and also has the following characteristics:                Easy to be regenerated for being used on different cycles,        Stability to be used repeatedly,        Immiscible with naphtha,        Do not contaminate the fuel,        Non-toxic, and        Friendly with environment        
To this end different ionic liquids were studied to find extractants for EDS [Bosmann A. et al. Chem Commun. 2001, 2494; Eber J. et al. Green Chem 2004, 6, 316, Zhang S. Ind. Eng Chem Res 2004, 43, 614; Niel Y. Energy Fuels. 2006, 20, 2083, J. Holbrey Green Chem 2008, 10, 87, R. Schmidt Energy Fuels. 2008, 22, 1774; Hee N. et al. Energy Fuels. 2008, 22, 1687, Xiang X. et al. Fuel 2008, 87, 79, Liu D. et al. Pet. Sci. Tech 2008, 26, 973, U.S. Pat. No. 7,001,504, CA Patent 02426770, CA Patent 02465374] and the analysis of experimental results has been concluded that they are very efficient extracting of sulfur compounds and also meet most of the above requirements.
Ionic liquids (IL) were developed in the early seventies and were focused mainly on battery development. Subsequently, they entered in different field in emerging scientific research due to their physicochemical characteristics, among others, having almost no vapor pressure, low toxicity and high temperatures of decomposition. For the above qualities, ionic liquids are considered as substances environmentally friendly or green solvents.
Deep desulfurization through liquid-liquid extraction using immiscible IL fuels is a potential application to be implemented in refineries, taking into account: the proven capacity of desulphurization technology, that extraction process is fully established, the immiscibility with naphtha and its ability to be recovered for reuse in multiple cycles of extraction.
The recovery of the IL that are used in extractive desulfurization is perhaps the most difficult to overcome for these substances have a brighter future in the implementation in refineries with a comprehensive process of desulfurization. In addition, the IL are expensive substances, on average, the cost of production of small quantities is about $1000 per kg, and in cases reached to produce large quantities can be obtained costs by U.S. $20-30 Kg [U.S. Patent Publication No. 2004/0188350 A1]. For the above reasons, although IL has deep desulfurization capacity, there is no clear industrial application without an attractive recovery process.
U.S. Pat. No. 7,001,504 B2 discloses several IL for desulfurization of hydrocarbons, IL including anions of the type Chloroaluminates (AlCl4−), states that the ionic liquids are feasible to recover through different techniques among which include heating of IL for the evaporation of sulfur compounds, removal of sulfur compounds from the IL using another solvent, distillation under reduced pressure, oxidation of sulfur compounds present in the IL, supercritical extraction with CO2 or combination of any of these techniques.
Another way in the recovery of IL is the use of biocatalysts, which oxidize the sulfur compounds and are removed from IL through extraction with a polar solvent. [U.S. Pat. No. 5,910,440].
Mexican patent application [Mx/a/2008/011121 N. V. Likhanova, R. Martinez Palou and J. F. Palomeque Santiago] describes another procedure for IL recovery by successive extractions of sulfur compounds with different solvents. This procedure is successful when ionic liquids have organic anions and cations.
In other research, the process of IL recovery with dimethyl phosphate and diethyl phosphate anions, which were used for desulfurization of model gasoline, by dissolving in water of these IL and subsequent precipitation or crystallization. The precipitates and crystals of sulfur-free IL are separated by centrifugation. The sulfur compounds are tracked in water by high performance liquid chromatography, HPLC.
U.S. Patent Publication No. 2007/0249486 A1 discloses the regeneration of IL used as catalysts. Here, the catalytic activity of 1-buthylpyridinium heptachloroaluminate ionic liquid was regenerated using gold and hydrogen.
Other studies of deep desulfurization of naphtha by using highly effective IL removal of sulfur compounds, especially using IL-containing halogenoferrates or halogen aluminates as anions, do not present methods for recovery of ionic liquids.
The ILs with halogenoaluminates and halogenoferrates have efficiencies above 90% in the desulfurization of naphthas, or whatever it is, deep desulfurization of naphthas. The same IL can fulfill another important feature to be used as extractants in the desulfurization, which has very low miscibility with naphtha. Therefore it is necessary recovery and reuse of IL in several cycles of desulfurization.
Given all this, it is necessary to develop a recovery process for IL which are efficient in the extractive desulfurization of naphthas and implement as an alternative technology for desulfurization of fuels.
The process claimed in this invention represents an alternative for the recovery of exhausted ILs containing which are used in deep extractive desulfurization of naphthas and have desulfurization efficiencies up to 95%. Although the scope of this invention is not limited to such application and that this recovery process can be applied to halogenometallates the recovery of IL sensitive to the presence of water or other nucleophiles that undergo a process of decomposition.